In order to observe a fine region of an object, a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like is used. In general, in these apparatuses, a housing, in which a sample is disposed, is subjected to evacuation of air, an atmosphere of the sample is in a vacuum state, and then the sample is imaged. However, a biological or chemical sample, a liquid sample, or the like is damaged, or a state thereof is changed, in a vacuum state. On one hand, there have been increased needs for observing such samples by using an electron microscope and, recently, an SEM apparatus, in which an observation target sample can be observed under atmospheric pressure, has been developed.
PTL 1 discloses an SEM apparatus in which observation can be performed under atmospheric pressure. Since a diaphragm, which can transmit an electron beam, is provided between an electron optical system and a sample such that a vacuum state and an atmospheric state are separated in principle, this apparatus is different from an observation technique for an environmental cell or the like in that the sample approaches the diaphragm such that an observation is performed in a non-contact state.